1. Field of the Invention
This invention relates to antennas, and more particularly to a method for calibrating a phased array antenna and a calibrated phased array antennas.
2. Description of Related Art
Microwave terrestrial and satellite communications systems are rapidly being deployed to serve communications needs. In these systems, to ensure a radio communication link between a fixed station on the ground or on a satellite and a mobile station such as an automobile or airplane, antenna systems with scanning beams have been put into practical use. A scanning beam antenna is one that can change its beam direction, usually for the purpose of maintaining a radio link, e.g. to a tower or satellite, as a mobile terminal is moving and changing direction. Another application of a scanning beam antenna is in a point-to-multipoint terrestrial link where the beams of a hub antenna or remote antenna must be pointed in different directions on a dynamic basis.
Early scanning beam antennas were mechanically controlled. The mechanical control of scanning beam antennas have a number of disadvantages including a limited beam scanning speed as well as a limited lifetime, reliability and maintainability of the mechanical components such as motors and gears.
Electronically controlled scanning beam antennas are becoming more important with the need for higher speed data, voice and video communications through geosynchronous earth orbit (GEO), medium earth orbit (MEO) and low earth orbit (LEO) satellite communication systems and point-to-point and point-to-multipoint microwave terrestrial communication systems. Additionally, new applications such as automobile radar for collision avoidance can make use of antennas with electronically controlled beam directions.
Phased array antennas are well known to provide such electronically scanned beams and could be an attractive alternative to mechanically tracking antennas because they have the features of high beam scanning (tracking) speed and low physical profile. Furthermore, phased array antennas can provide multiple beams so that multiple signals of interest can be tracked simultaneously, with no antenna movement.
In typical embodiments, phased array antennas incorporate electronic phase shifters that provide a differential delay or a phase shift to adjacent radiating elements to tilt the radiated phase front and thereby produce farfield beams in different directions depending on the differential phase shifts applied to the individual elements or, in some cases, groups of elements (sub-arrays). Of course, there is a need to efficiently and effectively calibrate phased array antennas and, in particular, there is a need to efficiently and effectively calibrate phased array antennas that incorporate voltage tunable dielectric phase shifters. This need and other needs are satisfied by a method for calibrating a phased array antenna and a calibrated phased array antenna of the present invention.
The present invention includes a method for calibrating a phased array antenna and a calibrated phased array antenna. In the preferred embodiment of the present invention, the method for calibrating a phased array antenna containing a plurality of electronically tunable phase shifters includes the steps of: (a) positioning an RF receiver away from the phased array antenna such that the RF receiver can receive energy emitted from the phased array antenna; (b) setting each of the plurality of electronically tunable phase shifters in the phased array antenna to a random phase; (c) successively applying a plurality of tuning voltages to a first one of the phase shifters coupled to a first column of radiating elements in the phased array antenna to control the phase shift provided for the first column of radiating elements; (d) measuring the phase and amplitude of a signal transmitted from the first column of radiating elements in the phased array antenna to the RF receiver for each tuning voltage applied to the first phase shifter; (e) determining the phase shift versus tuning voltage data for the first column of radiating elements; (f) repeating steps (b), (c), (d) and (e) for each column of radiating elements of the phased array antenna; and (g) using the determined phase shift versus tuning voltage data to adjust the phase shift for each of the phase shifters to yield a uniform phase front at an aperture of the phased array antenna.